In the slicing of hard material ingots using abrasive slurries in wire saws, the cut disks/wafers coming out of the saw are surface saturated with glycol, or other water miscible or water compatible slurry from the abrasive cut. In most cases, the spaces between cut wafers are extremely small, measuring as low as ˜100 μm between surfaces, or lower. In order to further process and use the cut wafers/disks for any end purpose, the entire surface of the cut wafers must be rinsed clean of all residual abrasive slurry. Any remaining residue of slurry solids may negatively impact further processing of the cut wafers/disks, reducing final use efficiency and overall production yield of the slicing process.
It is generally believed that to increase water penetration, wetting along a solid surface or spreading of water, that surface tension of water needs to be greatly lowered below its ambient STP level of about 70 Dynes/cm. In general, such a procedure can be accomplished by the addition to the water of any one of many known surface active agents or detergents.
However, effective water rinsing of slurry from microscopic spaces must also be performed without foaming. Foaming presents a direct obstacle to liquid wetting and penetration into small or large spaces by the presence of gas entrapped membranes which block or inhibit liquid water from effective contact with said spaces, holes, cavities, etc.
Further, the suspension characteristics of all current abrasive slurries including those compatible, miscible or soluble in water, are known in the art to be quickly and significantly compromised upon the exposure to excess water. The result of this solids suspension effect is the abrasive solids within the slurry, upon exposure to “rinsing volumes” of water will agglomerate, then coagulate and quickly precipitate out onto the wafer or disk surface during the rinsing process. Once such solids precipitation has occurred, continuing rinsing with water will not effectively remove the precipitated solids, and the resulting “rinsed” wafers will be contaminated with precipitated slurry solids which can be impacted on the wafer surface making further processing difficult or impractical.
To avoid the above precipitation process during the rinse step, the water rinse must be both complete and mechanically faster than the solids precipitation process on exposure to excess rinse water from the slurry coating the wafers. To accomplish this, the water rinse must be extremely effective at penetrating, flowing through, and removing wafer surface slurry from even the microscopic spaces between the cut wafers. Further, the rinse water must be provided with a large amount of mechanical energy, most preferably in a uni-directional mode in order to “sweep” away the abrasive slurry before said solids precipitation can occur.
With a large amount of mechanical force applied to the water rinse flow, the presence of even low-foaming surface active agents will create sufficient “foaming” that will quickly and effectively inhibit rinsing speed and efficiency, particularly on free space constricted surfaces such as the sliced “kerf slots” between wafers on a cut ingot from a wire saw slicing process. This will result in a lower yield of clean, properly rinsed wafers from the slurry cut, and is highly undesirable. The preferred water rinse composition effectively has no tolerance for foaming at all, and all such propensity under high mechanical force/agitation must be eliminated to produce an effective water rinse composition.
The art contains a large number of effective “defoamers” that might be used. Among these are those materials or compounds in which foaming is not eliminated, or for which very large levels of the defoamer are required to completely eliminate foaming. Further, many defoamers also interfere with the surface tension lowering properties of the added surfactant system, or may reduce the wetting or penetration properties of the treated water system, thereby reducing the effectiveness of the surfactant composition in the rinse water.
Also, since the treated rinse water is typically discarded to drain, it is important that the environmental properties of the additive surfactant composition be human and environmentally friendly, with very low or non-existent toxicity. This requirement further limits the available materials to be selected that will also perform to the effectiveness level described herein.
It is desirable that the aqueous rinse composition have the following characteristics:    1. Lower the surface tension of water as a method of increasing water penetration and wetting on a solid surface.    2. Independent of surface tension, increase the wetting of water on a solid surface.    3. Perform (1) and (2) above without causing or initiating any foaming of the cutting liquid. Absence of foaming should be complete, even in the presence of violent agitation of the water mixture.    4. Create a composition that is human and environmentally friendly providing a water solution/mixture that is of very low toxicity or non-toxic.    5. Create a composition whose surface tension and surface wetting/penetration properties in mixture with water are not substantially affected by the presence of solid particle contamination.
U.S. Pat. No. 6,383,991 to Hashimoto, et al, discloses an aqueous cutting oil composition which contains a polyether compound and one or more surfactants, preferably a non-ionic surfactant. The cleaning process involves the use of water at an elevated temperature and then using the immersion method, ultrasonic cleaning, vibration and/or spraying to clean the wafers.
U.S. Pat. No. 6,221,814 to Kaburagi et al discloses an aqueous cutting liquid which comprises a hydrophilic alcohol such as ethylene glycol and a lipophilic compound such as propylene glycol which uses an organic solvent or water in the cleaning process.